Specific absorption rate (SAR) is a measure of the rate at which energy is absorbed by the human body when exposed to a radio frequency (RF) electromagnetic field. This measure has become increasingly important as mobile devices have become smaller and users have come to rely increasingly on such devices and use them close to their bodies. The United States and Europe have their own somewhat different standards, but the basic goal of protecting mobile device users from over exposure to RF energy is the same. To help monitor the RF field generated by a given device, a sensing pad or element may be disposed in the device to detect the level energy. A too high level of detected energy may trigger the device to reduce emitted power.
The integration of an antenna and sensing pad becomes increasingly problematic, however, as the mobile device itself becomes smaller and thinner since the sensing pad may detrimentally influence the performance of an antenna that is mounted nearby.
As an example, notebook computers are often designed with a keyboard component and a display component, connected via hinge, that can be opened and closed like a clamshell, or placed in a tablet configuration. In one possible configuration, the antenna might be disposed on an edge of the display component, and the sensing pad may be disposed on an edge of the keyboard component that is furthest from the edge in which the antenna is located. A problem occurs, however, when the notebook is configured in a tablet mode and the two edges, in which the antenna and sensing pad are respectively disposed, may be positioned close together. The proximity of the antenna and sensing pad may not only detrimentally influence the performance of the antenna, particularly in a low band, but may also impact accurately measuring SAR.